A modern architecture for a network switch comprises a multiplicity of modules, typically each provided on a respective silicon chip, wherein each module has a receiving section for processing data packets received on a multiplicity of ports, a switching section, which transmits those packets on one or other of a multiplicity of links, usually called ‘mesh’ links, and a transmitting section, which is connected to receive packets from a multiplicity of mesh links and provides for transmission of packets on one or other of a multiplicity of output ports. In a typical example, the switching section can direct packets to any one of four mesh links and the transmitting section can receive packets from any one of four mesh links.
One way of connecting such modules to form in effect a single switch is to connect one mesh link per module to the transmitting section of the same module and to connect each of the other three mesh links to a transmitting section in each of the other three modules. Although such a configuration is useful, it may be unsatisfactory where the modules have ports with an aggregate bandwidth capacity which is in excess of the link bandwidth, for example, if a module has 16 ports each having a data rate of 2.5 gigabits/sec, providing an possible aggregate of 40 gigabits/sec, and the links each have a maximum data rate of 10 gigabits/sec, there would be a severe loss of potential performance if for example most of the received traffic has to be directed to a particular link. The loss of performance would not be apparent if the traffic is evenly distributed to the four links, but such a distribution cannot be presumed.
It is known to couple a comparatively high-speed link, such as one having a 10-gigabit per second data rate, to a multiplicity of ports of a switch, of which the ports have a comparatively lower data rate, by means of a de-multiplexer or distributor. Thus for example a 10-gigabit per second link may be coupled to four ports each having a 2.5-gigabit per second data rate. Likewise, a group of transmit ports of the switch can be connected to a multiplexer which provides a common output on a comparatively high frequency serial link. Thus, for example, four transmit ports operable at a 2.5 gigabit per second rate may feed a common 10 gigabit per second link.